Portable electronic devices (e.g., mobile phones, media players, electronic watches, and the like) include a rechargeable battery that provides electrical power to operate the devices. In many such devices the battery can be recharged by coupling the electronic device to a power source through a physical connection, such as through a charging cord. Using a charging cord to charge a battery in an electronic device, however, requires the electronic device to be physically tethered to a power outlet. Additionally, using a charging cord requires the mobile device to have a connector, typically a receptacle connector, configured to mate with a connector, typically a plug connector, of the charging cord. The receptacle connector typically includes a cavity in the electronic device that provides an avenue within which dust and moisture can intrude and damage the device. Furthermore, a user of the electronic device has to physically connect the charging cable to the receptacle connector in order to charge the battery.
To avoid such shortcomings, wireless charging devices have been developed to wirelessly charge electronic devices without the need for a charging cord. For example, the battery in some electronic devices can be recharged by merely resting the device on a charging surface of a wireless charging device. A transmitter coil disposed below the charging surface may produce a time-varying magnetic flux that induces a current in a corresponding receiving coil in the electronic device. The induced current can be used by the electronic device to charge its internal battery.
Some existing wireless charging devices and electronic devices configured for wireless charging have a number of disadvantages. For instance, some wireless charging devices generate an unintended voltage on a receiving coil. The unintended voltage can create noise in the electronic device within which the receiving coil is housed. The noise can cause disturbance of sensitive electronic components in the electronic device, such as touch-sensitive components like a touch-sensitive display. As another example, while being charged, some electronic devices generate an unintended voltage on a transmitter coil in the wireless charging device. The unintended voltage can cause inefficiencies in the wireless power transfer. Additionally, the receiver coil and other components that are required for an electronic device to wirelessly receive power from a wireless charging device require a certain amount of real estate in the electronic device and can undesirably increase a thickness of the electronic device as compared to a similar device without a receiver coil and its associated components.